Browserify エラーを出す

#Browserify エラーを出す

gulpでbrowserifyを使いbuildしてエラーだった時

```
events.js:85
      throw er; // Unhandled 'error' event
```

と表示される

これだとどこがエラーなのかわからないので、
エラーを適切に出力したい

```gulpfile.js
'use strict';

var browserify = require('browserify');
var source = require('vinyl-source-stream');
var gulp = require('gulp');


gulp.task('build', function(){
    browserify({
        entries: 'index.js',
        debug: true
    })
    .transform('babelify')
    .bundle()
    .on('error', function(err){   //ここからエラーだった時の記述
        console.log(err.message); 
        console.log(err.stack);
    })
    .pipe( source('bundle.js') )
    .pipe( gulp.dest('build') );
});


gulp.task('default', ['build']);
```

エラーになるjsファイルを用意

```index.js
alert('A');

alert('a'F');
```

gulpを実行

```zsh
[18:23:38] Using gulpfile /node_sample/gulpfile.js
[18:23:38] Starting 'build'...
[18:23:38] Finished 'build' after 37 ms
[18:23:38] Starting 'default'...
[18:23:38] Finished 'default' after 6.42 μs
/node_sample/index.js: Unexpected token (3:9) while parsing file: /node_sample/index.js
SyntaxError: /node_sample/index.js: Unexpected token (3:9)
  1 | alert('A');
  2 |
> 3 | alert('a'F');
    |          ^
  4 |
    at Parser.pp.raise (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/location.js:24:13)
    at Parser.pp.unexpected (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/util.js:91:8)
    at Parser.pp.expect (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/util.js:85:33)
    at Parser.pp.parseCallExpressionArguments (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/expression.js:334:12)
    at Parser.pp.parseSubscripts (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/expression.js:306:29)
    at Parser.pp.parseExprSubscripts (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/expression.js:277:15)
    at Parser.pp.parseMaybeUnary (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/expression.js:247:19)
    at Parser.pp.parseExprOps (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/expression.js:178:19)
    at Parser.pp.parseMaybeConditional (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/expression.js:160:19)
    at Parser.pp.parseMaybeAssign (/node_sample/node_modules/babelify/node_modules/babel-core/node_modules/babylon/lib/parser/expression.js:123:19)
```

エラーの箇所が出た
OK

#####ちなみにpackage.jsonと.babelrcとnodeのversionです

```package.json
{
  "name": "node_sample",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "babel-preset-es2015": "^6.1.18",
    "babel-preset-react": "^6.1.18",
    "babelify": "^7.2.0",
    "browserify": "^12.0.1",
    "gulp": "^3.9.0",
    "vinyl-source-stream": "^1.1.0"
  }
}
```

.babelrc

```.babelrc
{
  "presets": ["es2015", "react"]
}
```

```zsh
% node -v
v5.0.0
```